Comments (9)

Tariq Saleh

Hi, I want to share the following information; as far as I know, increasing the pixel size will decrease the spatial resolution. I'm quoting form the following link "Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution"

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John Honovich

That's true, assuming the imager size stays the same, simply because the total area is constantbut the size of the components (i.e., pixels) have expanded. Bigger pixels in the same space means fewer total pixels, i.e., spatial resolution.

Btw, this is a tautology:

"Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution"

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Jim Hall

So it's kinda like a shared fairy tale that all the manufacturers tell round the campfire? Who gets stuck holding the "short end" of the stick?

At the risk of being pesky, there is a mighty odd thing going on there in that thar chart, where whenever the inch size denominator is an integer, the diagonal measurement is an integer too, but in mm. I can't think of how the heck that could happen except by chance?

One more for the road, does that mean that a 1/4" sensor is will always be having the same aspect ratio, or is that chart just a one example of what it could be? Thanks for the lesson.

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Rukmini Wilson

Jim, I'm a little surprised at your surprise; after all you were the first person to answer a similar question correctly, (though looking back, you did say you "cheated" :)

I never really found a satisfactory answer to how it came to be, but I don't think it's to 'hoodwink' anybody. What I did learn was that 'back in the day' , way before IP cams, the CCD sensor was surrounded by some kind of vacuum tube (help tube expert!) thingy that made the diagonal size of the whole component "1/4 or whatever. But of course the active sensor size was smaller. Then they stopped using the tubes, and started making smaller packages, just because they could.

My guess us when that started, they had to agree on the active dimensions of the old packages, and for some reason (help, fab expert), did that in mm. And that married the even inches to the even mm. Maybe John or somebody knows more. But its just history that's unimportant now, and like Brian basically said the only thing you need to know is you is that you don't know the exact size by the fractional inch thing, its just a convention.

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Undisclosed #1

Objection: the explanation to the answer does not give us any better metric than pixel size, saying

Pixel size is rarely disclosed, so it is hard to use as a metric. One can estimate it by contrasting resolution and imager size.

But since resolution and imager size are almost always present, one can almost always derive it thru simple division. Or add the calculation to the camera calculator, it's as easy as PPF.

However, even with that, low light quality varies greatly depending on image processing

Image processing is not a metric.

and integrated IR usage.

Most cameras, according to the finder, do not have IR, and therefore this might be hard to use as a metric.

Also, strictly speaking IR removes the low-light condition by adding (IR) light. In the case of the (few) cameras with integrated visible light, we would probably not say it had 'good low-light performance', rather we would say it had a 'good light'.

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Undisclosed #1

On the other hand, imager sizes in surveillance do not vary that much, so even with notably different imager sizes, the FoV only changes moderately.

Just to note, the change in FoV width is directly proportional to the change in sensor width, and inversely to focal length. In the example, a 1/3 format sensor has 75% of the width of a 1/2 format sensor.

With an imager twice as wide you would have a FOV twice as wide as well.

With a focal length twice as long you would have a FOV half as wide.

Of course imager sizes don't vary any where near the degree focal lengths do, which makes focal length more of a practical determinant.

Axis has released their first IR multi imager, the P3717-PLE, a repositionable model listing 360° IR illumination and flexible positioning,...

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The world's leading video surveillance information source, IPVM provides the best reporting, testing and training for 10,000+ members globally. Dedicated to independent and objective information, we uniquely refuse any and all advertisements, sponsorship and consulting from manufacturers.